Radio paging system

ABSTRACT

A paging system including one or more pagers having a transmitting function. The pagers can transmit to a base station a response upward signal acknowledging reception of a paging signal, and a pager initiative signal through direct sequence spread spectrum modulation. The pager assigns different spreading codes to the response upward signal acknowledging the reception of the paging signal and the pager initiative signal, so that the base station can receive them independently.

TECHNICAL FIELD

The present invention relates to a two-way paging system capable ofcalling users carrying pagers by radio, and allowing them to sendmessages from their pagers to base stations. In the followingdescription, a signal from a pager to a base station is referred to asan “upward signal”.

BACKGROUND ART

FIG. 1 is a block diagram showing a two-way paging system, which appliesa direct sequence spread spectrum scheme to transmit upward signals frompagers to base stations. The paging system comprises a central station 3connected to a communications network 2; a plurality of (n) basestations 7-1-7-n connected to the central station 3; and pagers 8-1 and8-2 capable of carrying out radio communications with the base stations7-1-7-n.

The central station 3 comprises an accepting unit 10, encoder 11,spreading code assigner 12 and line terminal unit 13. The accepting unit10 is connected to the communications network 2, receives paging requestsignals from the communications network 2, and supplies them to theencoder 11. The encoder 11 converts the paging request signals and codenotification signals into paging signal sequences. The code notificationsignals are output from the spreading code assigner 12 to notify thepagers of spreading codes for the upward signals. The line terminal unit13 delivers the paging signal sequences to corresponding base stations.The line terminal unit 13 also receives the upward signals sent from thepagers through the base stations, collects them, and supplies them tothe accepting unit 10. Thus, the accepting unit 10 notifies thetelephone 1 or computer terminal 9 of a paging response through thecommunications network 2.

The base stations 7-1-7-n each comprise a line terminal unit 20,transmitter 21, spreading code memory 25 and receiver 24. The lineterminal unit 20 receives the paging signal sequences from the centralstation 3, and transfers them to the transmitter 21. The transmitter 21converts them to radio signals (electromagnetic waves), and transmitsthem at a frequency F1. The receiver 24 in each of the base stations7-1-7-n receives the upward signals from the called pagers that aredetecting the paging signals addressed thereto. The receiver 24 uses aplurality of spreading codes prestored in the spreading code memory 25for despreading these upward signals. The received upward signals aretransmitted through the line terminal unit 20 to the central station 3,so that it sends the response information to the telephone 1 or computerterminal 9 via the communications network 2.

Next, the operation will be described for paging the pager 8-1 or 8-2from the fixed telephone 1 or computer terminal 9. The user inputs tothe telephone 1 or computer terminal 9 the called number of the pager8-1 or 8-2, and a message if there is any. The input information is sentto the central station 3 through the communications network 2 as apaging request signal. In the central station 3, the encoder 11 convertsinto the paging signal sequence the paging request signal from theaccepting unit 10 and the code notification signal supplied from thespreading code assigner 12 to notify the called pager of the spreadingcode. The line terminal unit 13 transmits it to the base stations7-1-7-n. The base stations 7-1-7-n each convert it to a radio signal(electromagnetic wave), and transmit it simultaneously to their ownradio zones 5-1-5-n at the same frequency F1. The pagers 8-1 and 8-2each receive the radio signal at the predetermined frequency F1, andinforms the user of the pager when they detect the paging signal callingthem. After that, the pager 8-1 or 8-2 sends to the base stations apaging response it produces by the direct sequence spread spectrummodulation using the spreading code that is defined by the codenotification signal received in conjunction with the paging signal. Thebase station in the radio zone in which the pager is located despreadsthe upward signal using the spreading code prestored in the spreadingcode memory 25, and transmits it to the central station 3 (in theexample as shown in FIG. 1, the base station 7-1 receives the upwardsignal transmitted from the pager 8-1, and the base station 7-2 receivesthe upward signal transmitted from the pager 8-2). Thus, the centralstation 3 notifies the telephone 1 or computer terminal 9 via thecommunications network 2 that the pager accepts the call.

FIG. 2 illustrates a structure of the paging signal sequence sent fromthe base stations. The paging signal sequence is based on the signalstructure shown in the RCR STD-43 standard worked out by Association ofRadio Industries and Businesses in Japan. In this signal structure, thepaging signal sequence consists of frame sequences each of whichincludes m successive frames as shown in FIG. 2(a). Each frame has asignal length of Tf, and consists of a synchronization signal and psubframes as shown in FIG. 2(b) which illustrates the i-th frame (1≦i≦m)as an example, which will be called “frame i” from now on. Here, prepresents the number of times of transmissions of the same pagingsignal. Each subframe of the frame i includes an address field, vectorfield and message field: The address field consists of qji (1≦j≦p)address signals; the vector field consists of qji vector signalscorresponding to the address signals; and the message field consists ofqji message signals corresponding to the address signals as shown inFIG. 2(c) which illustrates the p-th subframe. A vector signal k(1≦k≦qji) indicates the start point and end point of a message signal kcorresponding to an address signal k. With such a signal structure, thecode notification signal is affixed to an initial position of eachmessage signal in the message field.

Thus, the subframe p in the frame i in the paging signal sequence hasqpi paging signals inserted thereinto, wherein k-th (1≦k≦qpi) pagingsignal is provided with the code notification signal Cuk indicative ofthe spreading code used for generating the upward signal by the directsequence spread spectrum modulation. When the pager, to which the framei is assigned to be received, detects its own paging signal in the framei during the transmission period Tf beginning from time t0, it starts totransmit the response upward signal corresponding to the paging signalfrom time t0+Tf at the earliest. FIG. 2(d) illustrates an example inwhich it transmits the upward signal during time t0+2Tf-t0+3Tfconsidering the processing delay and the like required for receiving andtransmitting the signal.

FIG. 3 is a block diagram illustrating a configuration of the pager. Itcomprises a receiver 30, controller 31, speaker 32, driver 33, display34 and transmitter 35. The transmitter 35 is a direct sequence spreadspectrum modulation transmitter. The receiver 30 is brought into areceiving state only during a receiving period of one or morepreassigned frames among the paging signal sequences transmitted fromthe base station, and receives the frames. This technique, which iscalled an intermittent receiving method, can prolong the life of thebattery of the pager. The controller 31 checks whether its own pagingsignal is present or not in the received frame, and notifies, if it isdetected, the user that a call takes place, by a beep from the speaker32 or some other alarms. If the paging signal includes a message, thecontroller 31 displays it on the display 34 via the driver 33. Then, thecontroller 31 supplies the transmitter 35 with a response upward signalcorresponding to its own paging signal detected, together with aspreading code uniquely determined by the code notification signalcontained in the paging signal. The transmitter 35 carries out, usingthe spreading code fed from the controller 31, the direct sequencespread spectrum modulation of the upward signal which is also fed fromthe controller 31, and transmits it to the base station. In this case,the frequency Fb for transmitting the upward signal is uniquelypredetermined from the frequency F1 for receiving the paging signal.

FIG. 4 illustrates an example of the upward signal composed of thesynchronization signal, pager ID (identification) signal and responseinformation acknowledging reception of the paging signal.

If two pagers, which receive the same forward signal frequency Fl,receive paging signals transmitted in the same frame, they willsimultaneously transmit their upward signals using the same frequencyFb. If the two pagers belong to different radio zones as shown in FIG.1, the two upward signals will be received without collision. Incontrast with this, the upward signal from the pager 8-2 can collidewith that from the pager 8-1, if it arrives at the base station 7-1 fromthe pager 8-2 located in the contiguous radio zone 5-2, or if it arrivesat the base station 7-1 because the pager 8-2 moves to the radio zone5-1 after receiving the paging signal sequence. Even in such a case,however, the upward signals can be received distinctly because thespreading codes determined by the code notification signals differ fromeach other, and are all known by the base station 7-1 because they areprestored in the spreading code memory 25.

DISCLOSURE OF THE INVENTION

The pager with the function to transmit the upward signal is applicablenot only to respond to the paging signal, but also to transmitinformation to another pager or a telephone or computer connected to thecommunications network, or to transmit information for its locationregistration. Such transmitting operation of the pager other thantransmitting the response upward signal is referred to as “pagerinitiative” from now on.

An object of the present invention is to provide a two-way paging systemenabling the base station to receive the response upward signalacknowledging reception of the paging signal, and the pager initiativeupward signal, independently.

There is provided a paging system having one or more base stations fortransmitting to a radio zone a paging signal sequence, and one or morepagers for receiving at least one paging signal of the paging signalsequence transmitted from the one or more base stations,

the pagers each comprising:

response means for transmitting, when the paging signal sequencereceived includes a paging signal addressed to the pager, a responsesignal acknowledging reception of the paging signal, through directsequence spread spectrum modulation; and

initiative transmission means for transmitting a pager initiative signalthrough direct sequence spread spectrum modulation using a spreadingcode different from that used by the response means, and

the base stations each comprising:

receiving means for receiving, from the response means and theinitiative transmission means of the pagers, signals that undergo thedirect sequence spread spectrum modulation.

According to the present invention, different spreading codes areassigned to the response upward signal acknowledging the reception ofthe paging signal and to the pager initiative upward signal. Thisenables the base station to receive the two types of upward signalsindependently even if they collide with each other, thereby improvingtheir transmission quality.

Here, the paging signal sequence transmitted from the base stations mayinclude information designating a spreading code used for transmittingthe response signal;

each of the pagers may further comprise code detection means fordetecting from the paging signal sequence the spreading code designated;and

the response means of the pager may carry out the direct sequence spreadspectrum modulation using the spreading code the code detection meansdetects.

The pagers may comprise a spreading code memory for storing a secondgroup of spreading codes different from a first group of spreading codesused by the response means; and

the initiative transmission means may carry out initiative transmissionby selecting a spreading code from the spreading code memory.

The pagers may comprise a spreading code memory; and

the initiative transmission means may carry out an initiativetransmission by selecting from the spreading code memory a spreadingcode other than the spreading code the code detection means detects.

The base stations may further comprise a spreading code memory thatstores entire spreading codes used; and

the receiving means may receive signals from the response means and theinitiative transmission means in each of the pagers by using thespreading code memory.

The base stations may further comprise a memory for storing thespreading codes designated for the pagers, and a spreading code memorythat stores the second group of the spreading codes; and

the receiving means may receive, using the memory and the spreading codememory, signals from the response means and the initiative transmissionmeans in the pagers.

The base stations may further comprise a memory for storing spreadingcodes designated for the pagers, and a spreading code memory that storesentire spreading codes use; and

the receiving means may receive, using spreading codes from the memoryand spreading codes from the spreading code memory excluding thosestored in the memory, the signals from the response means and theinitiative transmission means in each of the pagers.

The spreading codes used by the initiative transmission means may beselected at random.

The initiative transmission means may transmit, as its transmittingsignal, at least one of a reply to a message from a user and a locationregistration signal.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a block diagram showing a conventional two-way paging system;

FIG. 2 is a diagram showing a structure of a paging signal sequencetransmitted from a base station;

FIG. 3 is a block diagram showing an example of a pager;

FIG. 4 is a diagram illustrating a structure of an upward signal;

FIG. 5 is a block diagram showing a paging system in accordance with thepresent invention;

FIG. 6 is a block diagram showing a configuration of a pager;

FIG. 7 is a diagram illustrating an assignment example of spreadingcodes;

FIG. 8 is a flowchart illustrating the operation of a spreading codeassigner;

FIG. 9 is a flowchart illustrating the operation of a controller;

FIG. 10 is a diagram illustrating the transmission timings of a pagerinitiative upward signal and an upward signal acknowledging reception ofa paging signal in conjunction with the receiving timings of the pagingsignal;

FIG. 11A is a block diagram showing a configuration of a base station;

FIG. 11B is a diagram illustrating spreading codes in a memory 23 andspreading code memory 25;

FIG. 12 is a flowchart illustrating control operation by a controller;

FIG. 13A is a block diagram showing another configuration of the basestation;

FIG. 13B is a diagram illustrating spreading codes in a memory 23 andspreading code memory 25;

FIG. 14 is a diagram illustrating a sequence for transmitting the pagerinitiative upward signal; and

FIG. 15 is a diagram illustrating another sequence for transmitting thepager initiative upward signal.

BEST MODE FOR CARRYING OUT THE INVENTION

Embodiment 1

FIG. 5 is a block diagram showing a paging system in accordance with thepresent invention, and FIG. 6 is a block diagram showing a configurationof a pager. The paging system comprises a central station 3 forgenerating paging signal sequences to be delivered; one or more basestations 4-1-4-n for transmitting the delivered paging signal sequencesto radio zones, and pagers 6-1 and 6-2 for receiving at least one pagingsignal in the paging signal sequences transmitted from the base stations4-1-4-n.

The central station 3 comprises an accepting unit 10, encoder 11,spreading code assigner 12 and line terminal unit 13. In the centralstation 3, the spreading code assigner 12 assigns spreading codes byselecting them from a group of spreading codes for transmitting responseupward signals which will be described later.

The base stations 4 each comprise a line terminal unit 20, transmitter21, receiver 24 and spreading code memory 25 as in the conventionalsystem as shown in FIG. 1. To receive the above mentioned pagerinitiative signals by the receiver 24, the spreading code memory 25stores not only the spreading codes for the response upward signalscorresponding to the paging signals, but also the spreading codes forthe pager initiative upward signals.

The pager 6-1 or 6-2 as shown in FIG. 6 comprises as the conventionalone a receiver 30, controller 31, speaker 32, driver 33, display 34,transmitter 35, and spreading code memory 36 for independently managingthe group of the spreading codes for transmitting the response upwardsignal, and that for transmitting the pager initiative upward signal. Inaddition, it comprises an input unit 37 for inputting responses tomessages or the like, and an interface unit 38 for delivering theinformation from the input unit 37 to the controller 31.

With the foregoing arrangement, the pager 6-1 and 6-2 can each transmit,through the direct sequence spread spectrum modulation, the responseupward signals, which acknowledge that the pagers receive the pagingsignals address to them when the received paging signals include them,and the pager initiative upward signals, which are sent using spreadingcodes different from those associated with the response upward signals.More specifically, the spreading code memory 36 in each pager managesthe spreading codes to be used in the direct sequence spread spectrummodulation carried out by the transmitter 35, by dividing them into twogroups in advance. The controller 31 selects, when transmitting theresponse upward signal, the spreading code to be used by the transmitter35 from a first group sent from the base station, and selects, whentransmitting the pager initiative upward signal, from a second group ofthe two groups stored in the spreading code memory 36.

FIG. 7 illustrates an example of the assignment of the spreading codes,in which r spreading codes available for the direct sequence spreadspectrum modulation are divided into two groups S1 and S2. The group S1includes h (0<h<r) spreading codes, and the group S2 includes theremaining r−h spreading codes. Assuming that Gold code sequences areapplied, and that the M-sequence for generating them has a period of2k−1, the sum total of 2k+1 spreading codes are present, which meansthat r=2k+1 (see, Yamauchi, “Spread spectrum communications—for the nextgeneration high performance communications—”, Tokyo Denki university,1994). The pager selects, when transmitting the response upward signalswhich acknowledge reception of the paging signal, the spreading codesfrom the group S1 for carrying out the direct sequence spread spectrummodulation, whereas it selects them from the group S2 for carrying outthe direct sequence spread spectrum modulation of the pager initiativeupward signal. This makes it possible to prevent the same spreading codefrom being used for modulating the two types of the upward signals.

The operation for assigning the spreading codes will now be describedwith reference to the flowcharts of FIGS. 8 and 9. It is assumed in theconfiguration shown in FIGS. 5 and 6 that the spreading codes in thegroup S1 are used to be assigned by the assigner 12 in the centralstation 3, whereas the spreading codes in the group S2 are used fortransmitting and receiving the pager initiative upward signal by storingthem in advance in the spreading code memory 36 in each of the pagers6-1 and 6-2, and in the spreading code memory 25 in each of the basestations 4-1-4-n.

With reference to the flowchart of FIG. 8 illustrating the operation ofthe spreading code assigner 12 in the central station 3, when insertingthe code notification signal (“YES” at S802), the spreading codeassigner 12 selects from the group S1 of FIG. 7 the spreading code to benotified (S804). The spreading code is selected such that it becomesunique in the same group (that is, in the same frame) of the targetpagers (but it can be not unique between frames). Then, the spreadingcode assigner 12 outputs the code notification signal corresponding tothe selected spreading code (S806). The code notification signal isencoded by the encoder 11 together with the message, and is transmittedto the base stations 4-1-4-n.

The base stations 4-1-4-n transfer the received encoded signal to thepagers through the transmitter 21.

With reference to the flowchart of FIG. 9 illustrating the operation ofthe controller 31 of the pagers 6-1 and 6-2, when transmitting theresponse upward signal acknowledging reception of the paging signal(“YES” at S902) after receiving it, the controller 31 sets to thetransmitter 35 the spreading code obtained from the information affixedto the paging signal addressed thereto, that is, the one the spreadingcode assigner 12 assigns in the central station 3 (S904). In contrastwith this, when transmitting the pager initiative upward signal (“YES”at S908), it sets the spreading code selected from the group S2 of FIG.7, which is stored in the spreading code memory 36 (S910). Then, itcommands the transmitter 35 to transmit the upward signal (S912).

The receiver 24 in each base station 4-1-4-n receives the responseupward signal using the spreading codes in the group S1 stored in thespreading code memory 25, and the pager initiative upward signal usingthe spreading codes in the group S2 which are also stored in thespreading code memory 25.

Thus assigning the spreading codes makes it possible for the responseupward signal sent from the pagers 6-1 and 6-2 for acknowledging thereception of the paging signal, and for the upward signal sent on theinitiative of the pagers 6-1 and 6-2, to use different spreading codesso that the receiver 24 can distinguish these upward signals. Thus, theupward signals can be transmitted without corrupting the transmissionquality.

FIG. 10 illustrates transmitting timings of the upward signalstransmitted on the initiative of the pagers, and those of the upwardsignals in response to the paging signal, in conjunction with thereceiving timings of the paging signals. As in FIG. 2, it is assumedhere that the subframe p in the frame i in the paging signal sequenceincludes qpi paging signals inserted thereinto, wherein k-th (1≦k≦qpi)paging signal is provided with the code notification signal k indicativeof the spreading code Cuk used for generating the direct sequence spreadspectrum modulation upward signal. The response upward signals for thepaging signals are the same as those of FIG. 2. FIG. 10 illustrates thecase where y pager initiative upward signals are transmitted from timet0+2Tf to t0+3Tf. They do not use spreading codes selected from thegroup of Cuk, but use spreading codes selected from the group S2, whichare denoted as Cgl (1≦l≦y).

If multiple upward signals are transmitted at the same timing on theinitiative of the pagers as shown in FIG. 10, each pager can generate arandom signal, and assign the spreading code based on the random signalto reduce the probability of using the same spreading code for theupward signal, or can assign the spreading code obtained from the randomsignal and its own address. Furthermore, when the base stations eachinsert in the paging signal sequence a base station identificationsignal which differs for each base station as disclosed in Japanesepatent application No. 8-167471(1996), each pager can assign thespreading code obtained from the ID signal and the random signal, orthat obtained from these plus its own address.

FIG. 11 shows another configuration of the base station in theembodiment 1, wherein FIG. 11A is a block diagram showing theconfiguration of the base station 4, and FIG. 11B is a diagramillustrating the spreading codes stored in the memory 23 and spreadingcode memory 25 of FIG. 11A.

The base station 4 as shown in FIG. 11 comprises a line terminal unit20, transmitter 21, code notification signal detector 22, memory 23,spreading code memory 25 and receiver 24. The line terminal unit 20,receiving the paging signal sequence from the central station 3,delivers it to the transmitter 21 and code notification signal detector22. The code notification signal detector 22 detects from the suppliedpaging signal sequence the code notification signals, and stores them inthe memory 23. The transmitter 21 converts the paging signal sequenceinto a radio signal, and transmits it at frequency F1. Thus, the memory23 stores the spreading codes used for despreading the response signalsfrom the pagers. The spreading code memory 25, on the other hand,prestores the group S2 of the spreading codes used for the pagerinitiative upward signals. FIG. 11B illustrate this. The memory 23stores the sum total of a spreading codes C′1-C′a (1<a≦h) detected bythe code notification signal detector 22, and the spreading code memory25 stores in advance the group S2 of the spreading codes used fordespreading the pager initiative upward signals.

In the base station 4, the receiver 24 receives the upward signals sentfrom the pagers using the memory 23 and spreading code memory 25: Toreceive the response upward signals, it uses the spreading codes storedin the memory 23, and to receive the pager initiative upward signals, ituses the spreading codes stored in the spreading code memory 25.

Although the ratio between the numbers of the spreading codes in thegroups S1 and S2 is fixed in the foregoing example, and the spreadingcode memories 25 and 36 store the spreading codes different from thoseassigned by the spreading code assigner 12, they can store the samespreading codes, and the ratio of the numbers of the spreading codesstored in the groups S1 and S2 can be varied from frame to frame thattransmit the upward signals.

Embodiment 2

The foregoing embodiment has a dividing loss involved in separating theavailable spreading codes into the two groups. For example, when thetraffic of the response upward signals the pagers transmit toacknowledge the paging signals is large, and that of the pagerinitiative upward signals is small, a case can take place that thespreading codes to be assigned to the response upward signals lack,although those to be assigned to the pager initiative upward signals areleft unused, thereby preventing effective use of the spreading codes.

In view of this, it is preferable to use, as spreading codes to beassign to the pager initiative upward signals, spreading codes otherthan those designated by the information included in the received pagingsignals. More specifically, if there are r spreading codes that areavailable for the direct sequence spreading spectrum modulation in theconfiguration as shown in FIGS. 5 and 6, the spreading code assigner 12in the central station 3 selects and assigns any one of the r spreadingcodes. In addition, these r spreading codes are all stored in thespreading code memory 25 of the base stations 4-1-4-n and in thespreading code memory 36 of the pagers 6-1 and 6-2 so that the spreadingcodes that are not assigned to the current frame by the spreading codeassigner 12 can be used for transmitting or receiving the pagerinitiative upward signal. This will be described with reference to FIG.10. The spreading codes, which are used for the response upward signalsacknowledging the reception of the paging signals from time t0+2Tf tot0+3Tf, are Cu1, Cu2, Cuqpi. Accordingly, the pagers that transmit thepager initiative upward signals in the same interval receive the pagingsignals from time t0 to t0+Tf, recognize the spreading codes (Cu1, Cu2,. . , Cuqpi), and assign only the spreading codes which differ from therecognized spreading codes and are selected from those available for thedirect sequence spread spectrum modulation. FIG. 12 illustrates thecontrol flow by the controller 31 in each pager.

In FIG. 12, when the pager receives the paging signal addressed thereto(“YES” at S1202), it sets to the transmitter 35 the spreading code basedon the code notification signal added to the received message (S1204),and sends from the transmitter 35 the response upward signal thatundergoes the direct sequence spread spectrum modulation using the setspreading code (S1206). The operation so far is the same as that of FIG.9.

When transmitting the pager initiative upward signal (“YES” at S1208),the pager determines the interval to send it (frame i+2 as shown in FIG.10, for example), and receives the paging signals (those in the frame iof FIG. 10) that will cause the response upward signals in the intervaldetermined (S1210). Then, the pager recognizes the code notificationsignals in the received paging signals (S1212), selects, from among thespreading codes in the spreading code memory 36, a spreading code thatdiffers from those recognized, and sets it to the transmitter 35. Then,it commands the transmitter 35 to transmit the pager initiative upwardsignal (S1206). Thus, the transmitter 35 transmits the signal generatedthrough the direct sequence spread spectrum modulation using thespreading code.

The base stations can receive and despread the pager initiative upwardsignal using the spreading codes stored in the spreading code memory 25.

The foregoing spreading code assignment can apply different spreadingcodes to the response upward signals sent from the pagers 6-1 and 6-2 toacknowledge the reception of the paging signals, and to the pagerinitiative upward signals sent on the initiative of the pagers 6-1 and6-2, thereby preventing the transmission quality of the upward signalsfrom being degraded.

In this spreading code assignment, if multiple pager initiative upwardsignals occur in the same timing, a case can take place in which thesame spreading code is used by a plurality of upward signals as in theembodiment 1. To reduce the probability of such a timing, each pager cangenerate a signal at random and assign the spreading code obtained fromthe random signal as in the embodiment 1, or assign the spreading codeobtained from the random signal and the address of the pager.Alternatively, as disclosed in Japanese patent application No. 8-167471,which has not yet been published as of the application date of thepresent application, the pagers can assign, when the base stations eachtransmit different ID signals with inserting them in the paging signals,the spreading codes obtained from the ID signals and random signals, orthose obtained from them plus the addresses of the pagers.

FIG. 13 shows another configuration of the base station 4 in theembodiment 2, wherein FIG. 13A is a block diagram showing theconfiguration of the base station 4, and FIG. 13B is a diagramillustrating the spreading codes stored in the spreading code memory 25.

The base station 4 as shown in FIG. 13A comprises the line terminal unit20, transmitter 21, code notification signal detector 22, memory 23,spreading code memory 25 and receiver 24. The line terminal unit 20,receiving the paging signal sequence from the central station 3,delivers it to the transmitter 21 and code notification signal detector22. The code notification signal detector 22 detects from the suppliedpaging signal sequence the code notification signals, and stores thecorresponding spreading codes in the memory 23. The spreading codesstored in the memory 23 are supplied to the receiver 24. The output ofthe code notification signal detector 22 is also delivered to thespreading code memory 25 that stores the entire spreading codes. Thespreading code memory 25 can check the spreading codes fed from the codenotification signal detector 22, and supply the receiver 24 with thespreading codes other than those fed from the code notification signaldetector 22. The transmitter 21 converts the paging signal sequence intoa radio signal, and transmits it at frequency F1.

FIG. 13B illustrates the spreading codes supplied to the receiver 24from the memory 23 and spreading code memory 25. As shown in FIG. 13B,the memory 23 stores the total of a spreading codes C′1-C′a detected bythe code notification signal detector 22, and they are supplied to thereceiver 24. Although the spreading code memory 25 stores the entirespreading codes used, those that are supplied to the receiver 24 are thetotal of b spreading codes C″1-C″b excluding a spreading codes, wherea+b=r.

In the base station 4, the receiver 24 receives the upward signals sentfrom the pagers using the spreading codes supplied from the memory 23and spreading code memory 25: To receive the response upward signals, ituses the spreading codes supplied from the memory 23 which stores thetotal of a spreading codes for receiving the response upward signals asshown in FIG. 13B; and to receive the pager initiative upward signals,it uses the total of b spreading codes stored in the spreading codememory 25. Thus, since the base stations can each use differentspreading codes in the reception, they can positively receive theresponse upward signals by precedently demodulating the response upwardsignals which are likely to receive more often.

[Pager Initiative Upward Signal]

The following are example of applying the pager initiative upwardsignals.

(1) A pager originating response message to a received message.

(2) A location registration of the pager. These signals will now bedescribed in detail.

The response message here refers to a simple message the user of thepager sends in response to the received message. For example, readingthe received message, the user sends such a response message as“finished reading” or “OK” in response to the received message such as“we would like to meet you at six at Tokyo international air port”.

Next, the transmission of the pager for carrying out the locationregistration will be described. In FIG. 5, it is likely that serviceareas consist of the radio zones which have multiple frequencies F1 andF2, for example, and are operated independently. In this case, it isnecessary for each pager to register to the accepting unit its currentlocation. To achieve this, the pager initiative upward signal can beused.

In FIG. 5, let us assume that the pager 6-2 in the radio zone 5-2 movesto the radio zone 5-n having different frequencies, and that it canreceive both the frequencies F1 and F2. The pager 6-2 measures which ofthe two frequencies is received better. If it decides that the frequencyF2 is received better than F1 when it moves from the radio zone 5-2 to5-n, it transmits to the base station 4-n a location registrationrequest on its initiative. In response to this, the base station 4-nsends an acknowledgment of receiving the location registration request.From that time on, the central station 3 carries out the paging to thepager 6-2 through the area including the radio zone 5-n.

[Transmission Flow of the Pager Initiative Upward Signal]

A flow for carrying out the transmission of such a pager initiativeupward signal will now be described with reference to FIG. 14.

In FIG. 14, when transmitting the upward signal from the pager, it setsa signal to be sent (like a message or location registration signal),and executes the transmission on the pager initiative. Thus, thecontroller 31 of the pager starts the transmission control. First, ittransmits to the base station a transmission request (S1402). Thetransmission request signal is modulated using the spreading codeselected by means of the above selection.

The base station, as in the normal message transmission, transmits tothe pager the paging signal allowing the transmission, along with thecode notification signal for notifying the spreading code to be used forresponding (S1404). Receiving the transmission allowed signal, the pagertransmits in response to it the message (or location registrationsignal) to be transmitted (S1406). The response signal undergoes directsequence spread spectrum modulation using the spreading code designatedby the code notification signal. The response signal also has thefunction of acknowledgment (ACK) in response to the transmission allowedsignal sent from the base station.

[Another Transmission Flow of Pager Initiative Upward Signal]

Another transmission flow of another pager initiative upward signal willbe described with reference to FIG. 15.

The pager, detecting that it moves into another zone by measuring atwhich frequency it can receive better, transmits the locationregistration request on its initiative (S1502). The transmission appliesthe spread spectrum modulation using the spreading code selected by theabove-mentioned spreading code selection. Receiving it, the base stationtransmits a paging signal as an acknowledgment signal (ACK) indicativeof receiving the location registration signal (S1504). From now on, thecentral station 3 carries out paging to the pager through the locationregistered radio zone.

The pager can also transmits a pager initiative message in a similarmanner. Preparing the message, the pager transmits a signal includingthe message (S1506), which undergoes the spread spectrum modulationusing the spreading code selected by the foregoing code selection. Inresponse to this, the base station sends the paging signal as theacknowledgment signal indicative of receiving the message (S1508).

The pager initiative transmission carried out in this way can reduce thenumber of steps as compared with the transmission flow as shown in FIG.14.

[Application of the Message From the Pager]

If the user of the pager can transmit a response message such as“finished reading”, a user originating a message can receive a morepositive reply. For example, the user of the pager can transmit thefollowing reply in response to the inquiry of the user originating themessage.

(1) If there is no response to the message: “In transmission now”.

(2) If there is a response to the message, but the user of the pager hasnot yet transmitted the pager initiative message of reply: “Not yetfinished reading”.

(3) If there is a response to the message, and the user of the pagertransmits the message such as “finished reading”: “Already finishedreading”.

In this case, if there is any message to be sent together, it can alsobe transmitted at the same time.

To transmit the message, various methods can be taken. For example, itis possible not only to reply the inquiry, but also to transmit aresponse message, if there is any, to the party directly. The directtransmission can be achieved by means of voice, or text data such aselectronic mail.

According to the present invention described above, the pager usesdifferent spreading codes for carrying out direct sequence spreadspectrum modulation of the response upward signal, which the pager sendsto acknowledge the reception of the paging signal, and of the pagerinitiative upward signal. This enables the base station to receive themeven if they collide with each other at receiving, thereby improving thetransmission quality of the upward signals.

What is claimed is:
 1. A paging system having one or more base stationsfor transmitting to a radio zone a paging signal sequence, and one ormore pagers for receiving at least one paging signal of the pagingsignal sequence transmitted from the one or more base stations, said oneor more pagers each comprising: response means for direct sequencespread spectrum modulating, when the paging signal sequence receivedincludes a paging signal addressed to the pager, a response upwardsignal acknowledging reception of the paging signal, and fortransmitting the modulated response upward signal; and initiativetransmission means for direct sequence spread spectrum modulating apager initiative upward signal by using a second spreading codedifferent from a first spreading code used by said response means, andfor transmitting the modulated pager initiative upward signal, saidpager initiative upward signal being an upward signal other than saidresponse upward signal; and said one or more base stations eachcomprising: receiving means for receiving both of said modulatedresponse upward signal from said response means and said modulated pagerinitiative upward signal from said initiative transmission means.
 2. Thepaging system as claimed in claim 1, wherein said paging signal sequencetransmitted from said base stations includes information designating aspreading code used for transmitting the response upward signal; whereineach of said pagers further comprises code detection means for detectingfrom said paging signal sequence the first spreading code designated;and wherein said response means of the pager direct sequence spreadspectrum modulates said response upward signal by using the firstspreading code detected by said code detection means.
 3. The pagingsystem as claimed in claim 2, wherein each of said pagers comprises apager spreading code memory; and wherein said initiative transmissionmeans transmits the pager initiative signal by selecting said secondspreading code other than the spreading code detected by said codedetection means from said pager spreading code memory.
 4. The pagingsystem as claimed in claim 3, wherein each of said base stations furthercomprises a memory for storing said first spreading code designated forsaid pagers, and a spreading code memory for storing all of said secondspreading codes to be used; and wherein said receiving means receives,using said first spreading code from said memory and said secondspreading code from said spreading code memory excluding said firstspreading codes stored in said memory, the response upward signal andthe pager initiative upward signal from said response means and saidinitiative transmission means in each of said pagers, respectively. 5.The paging system as claimed in claim 1 or 2, wherein each of saidpagers comprises a pager spreading code memory for storing a furthergroup of second spreading codes different from a group of firstspreading codes used by said response means; and wherein said initiativetransmission means transmits the pager initiative signal by selectingone second spreading code of said further group from said pagerspreading code memory.
 6. The paging system as claimed in claim 5,wherein each of said base stations further comprises a memory forstoring a group of said first spreading codes designated for saidpagers, and a spreading code memory for storing said group of saidsecond spreading codes; and wherein said receiving means receives saidmodulated response upward signal and said modulated pager initiativeupward signal and obtains said first and second spread codes from saidmemory and said spreading code memory, respectively.
 7. The pagingsystem as claimed in claim 1, wherein each of said base stations furthercomprises a spreading code memory that stores all of said secondspreading codes to be used; and wherein said receiving means receivessaid modulated response upward signal and said modulated pagerinitiative upward signal and obtains a second spread code from saidspreading code memory in response to said upward signals received. 8.The paging system as claimed in claim 1, wherein the spreading codesused by said initiative transmission means are selected at random. 9.The paging system as claimed in claim 1, wherein said initiativetransmission means transmits, as its pager initiative signal, at leastone of a reply to a message from a user and a location registrationsignal.
 10. A pager in a paging system that includes one or more basestations for transmitting to a radio zone a paging signal sequence, andone or more pagers for receiving at least one paging signal of thepaging signal sequence transmitted from the one or more base stations,said pager comprising: response means for direct sequence spreadspectrum modulating, when the paging signal sequence received includes apaging signal addressed to the pager, a response upward signalacknowledging reception of the paging signal and for transmitting themodulated response upward signal; and initiative transmission means fordirect sequence spread spectrum modulating a pager initiative upwardsignal by using a second spreading code different from a first spreadingcode used by said response means and for transmitting the modulatedpager initiative upward signal, said pager initiative upward signalbeing an upward signal other than said response upward signal.
 11. Thepager as claimed in claim 10, wherein said paging signal sequencetransmitted from said base stations includes information designating aspreading code used for transmitting the response upward signal; whereinsaid pager further comprises code detection means for detecting fromsaid paging signal sequence the first spreading code designated; andwherein said response means direct sequence spread spectrum modulatessaid response upward signal by using the first spreading code detectedby said code detection means.
 12. The pager as claimed in claim 11,further comprising a pager spreading code memory, wherein saidinitiative transmission means transmits the pager initiative signal byselecting said spreading code other than the spreading code detected bysaid code detection means from said spreading code memory.
 13. The pageras claimed in claim 10 or 11, further comprising a pager spreading codememory for storing a further group of second spreading codes differentfrom a group of first spreading codes used by said response means,wherein said initiative transmission means transmits the pagerinitiative signal by selecting one second spreading code of said furthergroup from said pager spreading code memory.
 14. The pager as claimed inclaim 10, wherein the spreading codes used by said initiativetransmission means are selected at random.
 15. The pager as claimed inclaim 10, wherein said initiative transmission means transmits, as itspager initiative signal, at least one of a reply to a message from auser and a location registration signal.